Trigger syntax on phptheadmin

phpmyadmintrigger

I can't make this work. I want to create a trigger that deletes the child foreign keys before I delete the parent primary key. This is the code that I am using on phpmyadmin:

delimiter // 
CREATE TRIGGER removeforeign  
before delete 
on products
FOR EACH ROW 
BEGIN 
delete from sales_details
where product_code=21; 
END// 
delimiter ;

Right now, I can't make trigger works at all. Not for insert, delete, update. In this code, it will delete where product_code is 21 because it's only an attempt to get the syntax right, I am still to figure it out how to compare with what is being deleted. Please, help me with the syntax. I can't see why it isn't working.

Best Answer

It may be more efficient to simply use a cascading delete via a foreign key. When a row with the same product_code is deleted from products, it will be deleted in sales_detail as well.

ALTER TABLE sales_details
ADD FOREIGN KEY fk_product_code(product_code)
REFERENCES products(product_code)
ON DELETE CASCADE;

But if you'd like to use a trigger to delete rows from the products table that have the same product_code as the row deleted, this should do the trick:

 delimiter // 
 CREATE TRIGGER removeforeing 
  BEFORE DELETE ON products
  FOR EACH ROW BEGIN
    DELETE FROM sales_details WHERE product_code = OLD.product_code;
 END// 
 delimiter ;

Edit

Per documentation,

Within the trigger body, you can refer to columns in the subject table (the table associated with the trigger) by using the aliases OLD and NEW. OLD.col_name refers to a column of an existing row before it is updated or deleted. NEW.col_name refers to the column of a new row to be inserted or an existing row after it is updated.

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